The Government of the United States has rights in this invention pursuant to Grant No. 04-6-158-44120 from the Department of Commerce.
1. Field of the Invention
This invention relates to a method for preparing alkyl glycosides of amino sugars.
2. Description of the Prior Art
Simple derivates of N-acetylglucosamine, the alkyl glucosaminides, alkyl 2-acetamidoglycopyranosides, or the alkyl glycosides of amino sugars as they are also called, are known to promote the growth of Lactobacillus bifidus (Zilliken, Archives of Biochemistry and Biophysics, 54, 392, 1954). In this application the .beta.-anomer, ##STR1## has been found to be the active substance, whereas the .alpha.-anomer, ##STR2## shows little or no activity (Poupard, Bacteriological Review, 37, 136, 1973).
The most commonly used method for the preparation of alkyl glycosides of amino sugars is the Fischer method which involves a one-step, acid-catalyzed reaction of the parent sugar with an appropriate alcohol (Langlois, Methods in Carbohydrate Chemistry, Whistler and Wolfrom, Eds., Academic Press, New York, 1963, Vol. 2, p. 83). This method produces good yields (70-80%) of the alkyl glucosaminide. However, the .alpha.-anomer predominates in the product and this is of little value in promoting growth of L. bifidus.
An alternate method of preparation is the Koenigs-Knorr method which involves a multi-step reaction with formation of the glycosyl halide as an intermediate (Conchie and Levvy, Methods in Carbohydrate Chemistry, ibid., p. 332). This method is more time-consuming and the yields of the alkyl glucosaminides are relatively low, but it has the advantage of producing larger proportions of the .beta.-anomer.
The use of azeotropic distillation to remove water formed in the reaction of anhydrous alcohol with simple hemi-acetals is known (Smith and Cristol, Organic Chemistry, Reinhold Publishing Corporation, New York, 1966, p. 400). However, there is no teaching or suggestion that such a process would influence the proportion of the complex chiral .alpha.- and .beta.-anomers formed in the synthesis of alkyl glycosides of amino sugars. Furthermore, there is no suggestion that the process would be successful in forming alkyl glycosides in the presence of competing hydroxyl groups in the amino sugars.
There is, therefore, a distinct need for a method of preparing alkyl glycosides of amino sugars which results in improved proportions of the .beta.-anomers in the reaction products, and such a method is a primary object of this invention.
It is a further object to provide a process for preparing alkyl glycosides of amino sugars requiring shorter reaction times, and which minimizes the caramelization of the amino sugars.